Along an assembly line, diapers and various types of other absorbent articles may be assembled by adding components to and otherwise modifying an advancing, continuous web of material. For example, in some processes, advancing webs of material are combined with other advancing webs of material. In other examples, individual components created from advancing webs of material are combined with advancing webs of material, which in turn, are then combined with other advancing webs of material. Webs of material and component parts used to manufacture diapers may include: backsheets, topsheets, absorbent cores, front and/or back ears, fastener components, and various types of elastic webs and components such as leg elastics, barrier leg cuff elastics, and waist elastics. Once the desired component parts are assembled, the advancing web(s) and component parts are subjected to a final knife cut to separate the web(s) into discrete diapers or other absorbent articles. The discrete diapers or absorbent articles may also then be folded and packaged.
During the assembly process, the absorbent article must be conveyed from one operation to the next operation. Due to high manufacturing speeds and an increasing need for control of the article, vacuum conveyors have been used to create a force upon the article as the article is conveyed and/or operated on. More specifically, vacuum conveyors may comprise a belt having a plurality of apertures aligned with slots in a deck. The slots may be fluidly connected with a vacuum source that allows air to be drawn in through the apertures, which in turn, helps hold the article in contact with the belt while being conveyed. However, the use of vacuum conveyors at high manufacturing speeds has presented several problems.
For example, some vacuum conveyors may be equipped with a belt that is driven by gears having straight teeth (or teeth that are oriented perpendicular to the direction of travel) that mesh with correspondingly oriented rows of teeth on the belt. The straight profile of the teeth along with the high speed of the manufacturing line may create a substantial amount of noise. Generally, higher manufacturing speed, larger teeth, and wider tooth profiles are associated with higher noise level. In some configurations, the noise level may become so great that remedial measures must be taken to reduce levels of noise in surrounding areas. For example, conveyors may be required to be housed within a sound insulation structure to protect workers.
Additionally, due to the straight profile of the teeth and the need to manufacture at high speeds, manufacturers may not be able to control the CD position of the belt to a high degree of precision. Other problems that may result from the use of high speed vacuum conveyors may include but are not limited to: mistrack of the belt with respect to the machine frame, mistrack of the apertures in the belt relative to apertures in an apertured deck surface, inability to maintain alignment between the apertures in the belt and the channels in the deck that provide a vacuum, limitations on the position of the tension elements internal to the belt relative to the desired vacuum pattern, breakage of the belt under load, excessive wear from V-guides used as tracking elements in a belt, delamination of facings, such as nylon fabric, on the second, deck facing surface of a belt. As referred to above, mistrack is defined as a relative difference in the cross machine direction between a predetermined target value and a value that is greater than or less than the predetermined target value. As such, during use the belt may need to be moved in the cross direction to maintain the required alignment, also referred to as the predetermined target value. Vacuum conveyors often require considerable set up to maintain belt alignment parallel to the longitudinal machine direction. Precision machining operations to minimize belt mistrack add considerable capital cost and complexity to conveyors.
It is to be appreciated that the use of angled teeth in place of the straight teeth may provide a reduction in noise levels and may align the conveyor belt to the conveyor drive and deck. Some available belts utilize multiple rows of angled teeth where each row abuts the adjacent row along the cross direction. However, utilizing a plurality of rows of angled teeth on the belt may present other difficulties. For example, multiple rows of angled teeth on either the belt or gears may not be disposed at a constant width in the cross machine direction, which may result in excessive forces acting internal to the belt. For example, having the belt fixed with a plurality of rows of angled teeth does not allow the belt to give in to or adjust to cross directional movement. In turn, cross directional repositioning of the belt to maintain proper alignment may exert cross directional forces on the belt, resulting in premature belt failure and/or excessive wear.
Thus, a need exists for a method and an apparatus for conveying absorbent articles that maintains a belt at a desired alignment in the cross machine direction while also providing relatively lower noise levels.